MID servers threads can hang due to SSH synchronization issues.
Lower the number of threads available for the MID server to run concurrent probes. See Set MID Server thread use in the product documentation.
Another possible workaround is to replace the j2ssh-core.jar file in the affected MID Servers' agent/lib folder and restart MID Servers. (You can back up the existing JAR file first by renaming it or moving it out of the lib folder.) Keep in mind the lib folder is overwritten when MID Servers are upgraded. If you put this workaround in place and then upgrade to a non-fixed version, you will need to re-implement the workaround or upgrade to fixed version.
Related Problem: PRB592016